In manufacturing integrated circuits, semiconductor wafers may be completely coated with one or more layers of materials such as silicon dioxide, silicon nitride, or a metal. The unwanted material is then selectively removed using one or more etching processes, for example, by etching through a mask. Sometimes various patterns are etched directly onto the semiconductor surface. For example, circular holes or grooves may be made where trench capacitors are to be formed. Most integrated circuit etching removes material in selected regions only and is carried out using a series of related processing steps. First, a semiconductor wafer is coated with an adherent and etch-resistant photoresist. The photoresist is then selectively removed to leave a desired pattern. Etching is then carried out to transfer the mask pattern to the underlying material. The photoresist is then removed (stripped) and the wafer is cleaned.
Possible kinds of etching include wet chemical, electrochemical, plasma etching, reactive ion etching, ion beam milling, sputtering, and high-temperature vapor etching. Plasma etching is now commonly used in fine-geometry applications such as the fabrication of semiconductor memory devices. As the integration density of semiconductor integrated circuits increases, it will be desirable to improve the controllability of such etching processes for forming specific shapes of etched features such as deep trenches, contact holes, and openings on a semiconductor wafer.